Why Use HARDWARE Appliances for SOFTWARE-Defined WAN?

Prayson Pate
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Enterprises are investigating software-defined WAN (SD-WAN) to save networking costs and gain application control. Hoping to increase customer retention, service providers are rolling out managed SD-WAN offerings. These initial service offerings rely on deploying closed and vendor-specific SD-WAN appliances at the customer site.

With so much buzz in the SD-WAN community, it is easy to forget that the “S” in SD-WAN stands for software. Given the availability of software virtual network functions (VNFs) for SD-WAN, why would we use closed hardware-centric appliances to deliver an innovative service?

SD-WAN Should Fit Into a Cloud-Centric Architecture

Operators know that deploying appliances to deliver SD-WAN is problematic. One issue is that using appliances ties a service to the infrastructure. Doing so is contrary to the service provider’s vision of being able to treat services like applications. In that cloud-centric model, services are defined, built, delivered and managed at the speed of software. This eliminates the need to change underlying hardware and frees us from worrying about its details. Using a VNF version of SD-WAN is much more consistent with that cloud vision.

Treat SD-WAN Like a Set of Network Functions, Not a Standalone Application

SD-WAN has a number of features that are useful for building private overlay networks. Deploying these in an appliance has two big drawbacks:

  1. Monolithic: The full set of SD-WAN functions are always included, even if unused in a given deployment. For example, a fiber-fed location with no backup may need the policy control and overlay tunneling capabilities of SD-WAN, but not the WAN optimization or hybrid WAN features. The inclusion of unneeded features may add cost or complexity to the deployment.
  2. Standalone: SD-WAN appliances tightly couple their functions to the VPN service, and are not available as components in a larger service offering.

Integrate SD-WAN with Universal Platforms

Service providers are replacing closed appliances with universal CPE (uCPE) platforms that are hosted on commercial off-the-shelf servers. These uCPE platforms enable the dynamic deployment of a wide variety of software VNFs, ultimately empowering service innovation and service on demand. Deploying a closed and vendor-specific appliance does not fit this universal model.


Eager to gain the benefits of innovation while reducing cost and power, operators are embracing cloud-centric technologies such as NFV, SDN, and SD-WAN. SD-WAN can fit into this vision, but only if it is deployed as SOFTWARE on an open platform. Anything else is a step backward to the bad old days of vendor lock-in.

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